The present invention relates to a hot melt adhesive. More particularly, the invention relates to an adhesive which has desirable adhesive properties and which facilitates recycling cellulosic (e.g., paper) products having the adhesive thereon.
Hot melt and pressure sensitive adhesives for cellulosic products are typically water insoluble and thus are difficult to remove during recycling such as during a repulping process. The repulping process typically comprises mixing water and paper, and the fibers are separated via mechanical action. The slurry may then be passed through screens and centrifugal cleaners to remove non-fibrous contaminants such as glass, metal, plastic, dirt, and other unwanted solid materials. After waste paper is repulped, it is formed into paper or paper board on the moving wire of a fourdrinier machine or on the cylinders of a cylinder machine, pressed and dried to remove the remaining water.
The failure to remove all of the water insoluble adhesive from the repulped paper results in papers of low quality, inconsistent composition, and non-uniform appearance and surfaces. Additionally, the sticky nature of the adhesive can create processing difficulties in commonly used automated machinery. Both of these problems are due to the fact that the adhesives tend to agglomerate and form globules commonly called "stickies."
Various solutions to the problem associated with hot melt and pressure sensitive adhesives have been suggested. For example, U.S. Pat. No. 3,891,584 to Ray-Chaudhuri et al. proposes a water dispersible hot melt adhesive comprising 75 to 95 parts of a graft copolymer of vinyl monomer and a water soluble polyalkylene oxide polymer, and 5 to 25 parts of a tackifying resin. U.S. Pat. No. 4,176,054 to Kelley proposes providing the adhesive with a magnetic or paramagnetic material integrated therein. These solutions have not, however, been widely embraced by the industry due to cost and unacceptable adhesive properties of the resulting hot melt adhesive.
It is therefore an object of the present invention to provide a hot melt adhesive which facilitates the recycling of cellulosic products bearing the adhesive.
Still another object of the present invention is to provide a hot melt adhesive which obviates the problems associated with the formation of stickies during recycling.
Another object of the invention is to provide a hot melt adhesive which is characterized by aggressive tack and good machining properties.